Cyclic alkylene carbonates may be obtained by contacting alkylene oxide with carbon dioxide in the presence of a suitable catalyst. Such a process has been described, for example, in EP-A-119840. In addition, the cyclic alkylene carbonate may be further reacted. A conventional further process comprises hydrolysis of the cyclic alkylene carbonate to produce a diol as is described in U.S. Pat. No. 5,847,189.
U.S. Pat. No. 6,407,279 discloses the integration of the above steps such that cyclic carbonate may be fed to the transesterification reaction zone without purification of the cyclic carbonate. U.S. Pat. No. 6,407,279 also describes that the elimination of the cyclic carbonate purification step causes elimination of two vacuum distillation columns and gives a yield benefit by eliminating losses of cyclic carbonate attributable to the purification steps. The carbonation reaction of U.S. Pat. No. 6,407,279 is carried out at a pressure in the range from about 500 psia to about 1000 psia while the transesterification reaction is carried out at a pressure of about 100 psia to 300 psia.